Tumors of the urinary bladder will be induced in rabbits by feeding 2-acetylaminofluorene or a nitrofuran carcinogen (FNT). The induced tumors will be characterized by microscopic methods. A study will be made for the purpose of determining whether there is a quantitative relation between the amount of N-hydroxy-AAf in the urine and the occurrence of urothelial tumors. A second study will be designed to determine whether any or all of the metabolites of 2-AAF are absorbed by the urothelium and whether the pattern of absorption is related to the occurrence of tumors. A third study will be designed to establish relations between foci of absorption or retention of metabolites and the occurrence of urothelial tumors induced either with 2-AAF or FNT. Finally, Clinical Urologists will be encouraged to apply the principles of the experimental animal study to the analysis of the analysis of the cause of tumors of the human urinary bladder.